1. Field of the Invention
The invention relates to an inertia sensitive device for use in controlling the revolution of a shaft such as that of a seat belt retractor.
2. Description of the Prior Art
Known retractors for the safety belts of vehicles comprise a device for controlling the locking of the retractor in the direction of rotation corresponding to the extraction of the strap of the belt. The devices become activated when the vehicle is subjected to a predetermined value of acceleration or deceleration. The device is arranged such that it also becomes activated to prevent the extraction of the strap when the vehicule turns over or is tilted over. The blockage of the retractor is generally caused by means of a lever or other pivoting element which acts as a ratchet adapted to cooperate with the teeth of a wheel or gear directly or indirectly connected to the shaft of the retractor. The movement of the ratchet is generally controlled by the displacement of an inertia mass (ball or pendulum) which cooperates with the ratchet.
As a result of the construction of the known devices, the threshold of the triggering of the locking of the retractor varies according to the direction of the acceleration or deceleration or further on the angle of tilt to which the device responds. In effect, the inertia mass (ball, pendulum or the like) cooperates directly with the ratchet at variable distances from its pivoting axis thus corresponding to different trigger thresholds. Numerous inconveniences are therefore encountered due to the fact that, if it is desired that the devices trigger at low responses thresholds, it is also necessary that the triggering take place for a value of the angle of inclination or for a value of acceleration or of deceleration independant of the direction.